Hard-carbon-film-coated substrate and apparatus for forming the same

ABSTRACT

A hard-carbon-film-coated substrate includes in stacked sequence a substrate, an intermediate layer, and a hard carbon film. The substrate consists of a metal or an alloy mainly composed of Ni or Al, or stainless steel. The intermediate layer is mainly composed of Ru, Si, Ge or carbon, or is a mixed layer including Ru, Si, or Ge mixed with at least one of carbon, nitrogen or oxygen, with a composition gradient across its thickness. An apparatus for forming the coated substrate especially includes means for forming the intermediate layer and means for forming the hard carbon film in the same vacuum chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate coated with a hard carbonfilm which is applicable to a cutter such as an electric shaver or athin-film head, and a method of and an apparatus for forming the same.

2. Description of the Background Art

In order to improve adhesion between a substrate such as a ceramicsubstrate or a silicon substrate and a diamond-like carbon film, it hasgenerally been proposed to form an intermediate layer between thesubstrate and the diamond-like carbon film. Japanese Patent Laying-OpenNo. 1-317197 (1989) discloses a technique of forming an intermediatelayer mainly composed of silicon on a substrate by plasma CVD, and thenforming a diamond-like carbon film on the intermediate layer. Theintermediate layer improves the adhesion of the diamond-like carbon filmto the substrate as compared with the case of directly forming adiamond-like carbon film on a substrate.

However, no studies have been conducted relating to the formation of anintermediate layer between a diamond-like carbon film and a substrate ofnickel (Ni), aluminum (Al) or stainless steel for application to acutter such as an electric shaver cutter.

On the other hand, an apparatus described in Japanese Patent Laying-OpenNo. 3-175620 (1991) is known for forming a hard carbon film by plasmaCVD. This apparatus is adapted to form a diamond-like carbon film, whichis a hard carbon film, on a substrate by bias plasma CVD employing anECR (electron cyclotron resonance) plasma CVD apparatus.

FIG. 12 typically illustrates such a conventional apparatus for forminga diamond-like carbon film. Referring to FIG. 12, microwave supply means1 generates a microwave that passes through a waveguide 2 and amicrowave inlet window 3 to be guided to a plasma generation chamber 4.This plasma generation chamber 4 is provided with a discharge gas inletpipe 5 for introducing a discharge gas such as argon (At) gas. Further,a plasma magnetic field generator 6 is provided around the plasmageneration chamber 4. Due to the action of a high-frequency magneticfield which is formed by the microwave and a magnetic field generated bythe plasma magnetic field generator 6, a plasma of high density isformed in the plasma generation chamber 4. This plasma is guided to avacuum chamber 8 in which a substrate 7 is arranged, along the magneticfield diverged by the plasma magnetic field generator 6.

The vacuum chamber 8 is provided therein with a reaction gas inlet pipe9 for introducing methane (CH₄) gas serving as a raw material gas. Themethane gas which is introduced into the vacuum chamber 8 by thereaction gas inlet pipe 9 is decomposed by action of the plasma, to forma carbon film. A high-frequency power source 10, with a frequency of13.56 MHz, for example, is provided externally of the vacuum chamber 8for applying a prescribed high-frequency voltage (RF voltage) to asubstrate holder 11, thereby developing a negative self-bias in thesubstrate 7. Ions travel in the plasma at a lower speed than electrons,and hence, unlike the electrons, the ions cannot follow the potentialdeflection during application of the RF voltage. Thus, a large quantityof electrons are emitted toward the substrate 7 due to application ofthe RF voltage, whereby a negative self-bias is developed in thesubstrate 7. Thus, positive ions contained in the plasma are drawn toform a diamond-like carbon film on the substrate 7.

In such a conventional apparatus, the substrate 7 is mounted on thesubstrate holder 11 which is provided in the vacuum chamber 8, andthereafter the vacuum chamber 8 is evacuated for forming a film. Thus,this apparatus can treat only one substrate, or two substrates at themost, in a single film forming operation.

In the conventional apparatus, further, discharge is also caused in thevicinity of a portion of the substrate that is mounted on the substrateholder, i.e. a portion of the substrate that is not to be provided witha film. This effect disadvantageously increases the temperature of thesubstrate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide ahard-carbon-film-coated substrate comprising a substrate of a metal oran alloy which is mainly composed of Ni or Al, or stainless steel, and ahard carbon film provided thereon, with excellent adhesion between thesubstrate and the hard carbon film.

Another object of the present invention is to provide a hard carbon filmforming apparatus that can simultaneously treat a plurality ofsubstrates in a single process while preventing excess temperatureincrease of the substrates, for effectively forming hard carbon films onthe substrates.

The concept of the hard carbon film according to the present inventionalso includes a crystalline carbon film or amorphous diamond-like carbonfilm.

A hard-carbon-film-coated substrate according to a first aspect of thepresent invention comprises a substrate consisting of a metal or analloy mainly composed of Ni or Al, or stainless steel, an intermediatelayer mainly composed of Ru formed on the substrate, and a hard carbonfilm formed on the intermediate layer.

According to the first aspect of the present invention, the intermediatelayer mainly composed of Ru is provided between the substrate and thehard carbon film. Adhesion between the substrate and the hard carbonfilm is improved by such an intermediate layer.

The intermediate layer is preferably a mixed layer of Ru and at leastone element of carbon, nitrogen and oxygen. The composition ratio ofsuch a mixed layer is preferably graded along its thickness. In otherwords, the mixed layer preferably has a graded composition structure orgradient with a higher Ru content closer to the substrate and a highercontent of carbon, nitrogen and/or oxygen closer to the hard carbonfilm.

A method of forming the diamond-like carbon film coated substrateaccording to the first aspect of the present invention comprises a stepof emitting ions of an inert gas toward a substrate arranged in a vacuumchamber while simultaneously emitting material atoms for forming anintermediate layer from an evaporation source toward the substratethereby forming an intermediate layer on the substrate, and a step ofsupplying a reaction gas containing carbon into the vacuum chamber forforming a plasma and emitting the plasma toward the intermediate layerthereby forming a hard carbon film on the intermediate layer.

A hard-carbon-film-coated substrate comprising an intermediate layerthat is a mixed layer of Ru and at least one element of carbon, nitrogenand oxygen can be formed by any of the following methods.

One method according to the first aspect of the present inventioncomprises a step of supplying a reaction gas containing carbon into avacuum chamber with a gradually increasing supply quantity for forming aplasma, and emitting the plasma toward a substrate arranged in thevacuum chamber while also emitting ions of an inert gas toward thesubstrate and simultaneously emitting material atoms for forming anintermediate layer from an evaporation source toward the substrate at agradually reducing evaporation rate thereby forming an intermediatelayer consisting of a mixed layer of the material atoms and carbon,nitrogen and/or oxygen on the substrate. The method further comprises astep of supplying a reaction gas containing carbon, nitrogen and/oroxygen into the vacuum chamber for forming a plasma, and emitting theplasma toward the intermediate layer thereby forming a hard carbon filmon the intermediate layer.

A hard-carbon-film-coated substrate according to a second aspect of thepresent invention comprises a substrate consisting of a metal or analloy mainly composed of Ni or Al, or stainless steel, an intermediatelayer mainly composed of Si or Ge formed on the substrate, and a hardcarbon film formed on the intermediate layer.

According to the second aspect of the present invention, an intermediatelayer mainly composed of Si or Ge is provided between the substrate anda diamond-like carbon film. Adhesion between the substrate and thediamond-like carbon film is improved by such an intermediate layer.

According to the second aspect of the present invention, theintermediate layer is preferably a mixed layer of Si or Ge and carbon,nitrogen or oxygen whose composition ratio is graded along itsthickness. The mixed layer preferably has a higher Si or Ge contentcloser to the substrate and a higher carbon, nitrogen or oxygen contentcloser to the hard carbon film.

When the hard-carbon-film-coated substrate according to the secondaspect of the present invention is used for an inner blade of anelectric shaver, the intermediate layer is preferably in a range of 50to 8000 Å in thickness.

When the hard-carbon-film-coated substrate according to the secondaspect of the present invention is used for an outer blade of anelectric shaver, on the other hand, the intermediate layer is preferablywithin a range of 50 to 4000 Å in thickness.

The effect of improving adhesion is reduced if the intermediate layer istoo thin, while no further improvement in the adhesion is achieved ifthe thickness is increased beyond the aforementioned range.

A method of forming the hard-carbon-film-coated substrate according tothe second aspect of the present invention comprises a step ofsputtering material atoms for forming an intermediate layer byirradiation with ions of an inert gas, thereby forming an intermediatelayer on a substrate arranged in a vacuum chamber. This method furthercomprises a step of supplying a reaction gas containing carbon into thevacuum chamber for forming a plasma and emitting the plasma toward theintermediate layer, thereby forming a hard carbon film on theintermediate layer.

One method according to the second aspect of the present inventioncomprises a step of supplying a reaction gas containing carbon, nitrogenor oxygen into a vacuum chamber with a gradually increasing supplyquantity for forming a plasma and emitting the plasma toward a substratearranged in the vacuum chamber while sputtering material atoms forforming an intermediate layer by irradiating the same with ions of aninert gas with a gradually reducing or decreasing amount of irradiation,thereby forming an intermediate layer consisting of a mixed layer of thematerial atoms and carbon, nitrogen or oxygen. This method furthercomprises a step of supplying a reaction gas containing carbon into thevacuum chamber for forming a plasma and emitting the plasma toward theintermediate layer, thereby forming a hard carbon film on theintermediate layer.

According to this method, it is possible to form an intermediate layerhaving a graded structure.

A hard-carbon-film-coated substrate according to a third aspect of thepresent invention comprises a substrate consisting of a metal or analloy mainly composed of Ni or Al, or stainless steel, an intermediatelayer mainly composed of carbon formed on the substrate, and a hardcarbon film formed on the intermediate layer.

According to the third aspect of the present invention, the intermediatelayer mainly composed of carbon is provided between the substrate and adiamond-like carbon film. Adhesion between the substrate and thediamond-like carbon film is improved by such an intermediate layer.

When the hard-carbon-film-coated substrate comprising a carbon thin filmas the intermediate layer is used for an inner blade of an electricshaver, the carbon thin film is preferably within a range of 50 to 8000Å in thickness, while it preferably has a thickness of 50 to 4000 Å whenthe hard-carbon-film-coated substrate is used for an outer blade of anelectric shaver.

The effect of improving adhesion is reduced if the intermediate layer istoo thin, while no further improvement in adhesion is achieved if thethickness is in excess of the aforementioned range.

A hard-carbon-film-coated substrate according to the third aspect can beformed by the method according to the second aspect of the presentinvention.

A method according to a fourth aspect of the present invention isadapted to form a hard carbon film on a substrate, and comprises a stepof generating a plasma of an inert gas by electron cyclotron resonance,a step of applying a high-frequency voltage to a substrate so that aself-bias developed in the substrate is not more than -20 V, and a stepof emitting the plasma of the inert gas toward the substrate through anopening of a shielding cover which is provided above the substrate whilesupplying a reaction gas containing carbon gas into the plasma forforming a hard carbon film on the substrate.

In the method according to the fourth aspect of the present invention,the inert gas is preferably Ar gas, and the reaction gas containingcarbon is preferably CH₄ gas. Such Ar gas and CH₄ gas are preferablysupplied at partial pressures of at least 1.0×10⁻⁴ Toor and not morethan 20.0×10⁻⁴ Torr.

A hard carbon film forming apparatus according to a fifth aspect of thepresent invention is adapted to form a hard carbon film on a substrate,and comprises a vacuum chamber, a substrate holder which is rotatablyprovided in the vacuum chamber, a shielding cover having an openingtherein, which is provided to enclose a peripheral surface of thesubstrate holder, plasma generation means for generating a plasma in thevacuum chamber and emitting the plasma toward the substrate through theopening, reaction gas inlet means for supplying a reaction gascontaining carbon into the plasma which is generated from the plasmageneration means, and a high-frequency power source for applying ahigh-frequency voltage to the substrate holder so that a self-bias whichis developed in the substrate goes negative.

A hard carbon film forming apparatus according to a sixth aspect of thepresent invention is adapted to form an intermediate layer on asubstrate for further forming a hard carbon film on the intermediatelayer, and comprises a vacuum chamber, a substrate holder which isrotatably provided in the vacuum chamber, a shielding cover having firstand second openings therein, which is provided to enclose a peripheralsurface of the substrate holder, plasma generation means for generatinga plasma in the vacuum chamber and emitting the plasma toward thesubstrate through the first opening, reaction gas inlet means forsupplying a reaction gas containing carbon into the plasma which isgenerated from the plasma generation means, a high-frequency powersource for applying a high-frequency voltage to the substrate holder sothat a self-bias which is developed in the substrate goes negative, andintermediate layer forming means provided in the vacuum chamber foremitting material atoms for forming an intermediate layer toward thesubstrate through the second opening.

An apparatus according to a seventh aspect of the present invention isan exemplary apparatus according to the sixth aspect, and ischaracterized in that the intermediate layer forming means comprises anevaporation source provided in the vacuum chamber for emitting thematerial atoms for forming an intermediate layer toward the substratethrough the second opening, and an ion gun for emitting ions of an inertgas toward the substrate through the second opening simultaneously withemission of the material atoms from the evaporation source.

An apparatus according to an eighth aspect of the present invention isanother exemplary apparatus according to the sixth aspect, and ischaracterized in that the intermediate layer forming means comprises atarget consisting of the material atoms for forming an intermediatelayer, which target is provided in the vacuum chamber for sputtering thematerial atoms toward the substrate through the second opening, and anion gun for emitting ions of an inert gas toward the target forsputtering the same.

In the apparatus according to the present invention, the plasmageneration means is preferably an electron cyclotron resonance plasmaCVD apparatus.

In the apparatus according to the present invention, the shielding coveris preferably separated from the peripheral surface of the substrateholder at a distance of not more than a mean free path of the gasmolecules, and more preferably 1/10 of the mean free path of the gasmolecules.

In the apparatus according to the present invention, the shielding coveris preferably maintained at a prescribed potential, and is morepreferably grounded.

In the apparatus according to the present invention, the material atomsfor forming an intermediate layer are atoms of Si, Ru, carbon or Ge, ora mixture of Si, Ru, carbon or Ge and at least one of carbon, nitrogenand oxygen, for example, and the hard carbon film is formed at leastindirectly on a substrate consisting of a metal or an alloy mainlycomposed of Ni or Al, or stainless steel, for example, through such anintermediate layer.

The apparatus according to the present invention comprises the substrateholder which is rotatably provided in the vacuum chamber. Therefore, itis possible to mount a plurality of substrates on the substrate holder,thereby increasing the number of substrates that can be treated with asingle evacuation.

In the apparatus according to the present invention, the shielding coveris provided to enclose the peripheral surface of the substrate, so thatthe plasma which is generated from the plasma generation means isemitted through the opening of the shielding cover for forming the hardcarbon film on the substrate. Due to such a shielding cover, it ispossible to prevent the occurrence of discharge at locations other thanthose where it is intended to form the film, thereby suppressing atemperature increase of the substrate.

A method of forming the hard-carbon-film-coated substrate according to aninth aspect of the present invention comprises a step of supplying agas containing material atoms for forming an intermediate layer into avacuum chamber for forming a plasma and emitting the plasma toward asubstrate thereby forming an intermediate layer on the substrate. Thismethod further comprises a step of supplying a reaction gas containingcarbon into the vacuum chamber for forming a plasma and emitting theplasma toward the intermediate layer thereby forming a hard carbon filmon the intermediate layer.

According to the sixth aspect of the present invention, the intermediatelayer forming means is provided for emitting the material atoms forforming an intermediate layer toward the substrate through the secondopening of the shielding cover. Therefore, it is possible to form theintermediate layer as well as the hard carbon film with a singleevacuation. Further, it is possible to control the formation of the hardcarbon film and that of the intermediate layer independently of eachother. Thus, it is possible to form the hard carbon film after a desiredintermediate layer is formed on the substrate.

Further, it is possible to control the material composition ratio of theintermediate layer as desired by alternately repeating deposition of thecarbon film by plasma CVD through the first opening and deposition ofthe material atoms for forming an intermediate layer through the secondopening. Thus, it is possible to bring the material composition ratio ofthe intermediate layer into a graded structure gradually approaching thecomposition of the hard carbon film toward the hard carbon film. Due toformation of the intermediate layer having such a graded structure, itis possible to further improve adhesion between the substrate and thehard carbon film.

In the apparatus according to the fifth aspect of the present invention,the substrate holder is provided in the vacuum chamber, so that a numberof substrates can be mounted on the substrate holder. Thus, it ispossible to increase the number of substrates that can be treated in asingle evacuation.

The shielding cover is provided around the substrate holder, whereby itis possible to prevent the occurrence of discharge in the vicinity of asubstrate portion other than that which is to be provided with the film.Thus, it is possible to form the film while maintaining the substrate ata low temperature, whereby it is unnecessary to consider the heatresistance of the substrate.

The apparatus according to the sixth aspect of the present invention isfurther provided with the intermediate layer forming means. Thus, it ispossible to form the intermediate layer on the substrate in a singleevacuation step.

Further, it is possible to change the material composition ratio of theintermediate layer by alternately forming thin films by the plasmageneration means and by the intermediate layer forming means andchanging the respective thin film forming conditions. Thus, it ispossible to form an intermediate layer having a graded structure,thereby further improving the adhesion between the substrate and thehard carbon film.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a hard carbon film formingapparatus in an embodiment according to the fifth aspect of the presentinvention;

FIG. 2 is a plan view showing a portion around a forward end of areaction gas inlet pipe provided in the embodiment shown in FIG. 1;

FIG. 3 illustrates the relations between film forming times andsubstrate temperatures in an example of the present invention andcomparative examples;

FIG. 4 is a schematic sectional view showing a hard carbon film formingapparatus in an embodiment according to the seventh aspect of thepresent invention;

FIG. 5 illustrates the relation between a film forming time and a CH₄flow rate in the formation of an intermediate layer having a gradedstructure with the apparatus of the embodiment according to the seventhaspect of the present invention;

FIG. 6 illustrates the relation between the film forming time and anevaporation rate in the formation of the intermediate layer having agraded structure with the apparatus of the embodiment according to theseventh aspect of the present invention;

FIG. 7 is a schematic sectional view showing a hard carbon film formingapparatus in an embodiment according to the eighth aspect of the presentinvention;

FIG. 8 illustrates the relation between a film forming time and a CH₄flow rate in the formation of an intermediate layer having a gradedstructure with the apparatus of the embodiment according to the eighthaspect of the present invention;

FIG. 9 illustrates the relation between the film forming time and an ioncurrent density in the formation of the intermediate layer having agraded structure with the apparatus of the embodiment according to theeighth aspect of the present invention;

FIG. 10 is a sectional view showing a diamond-like carbon film directlyformed on a substrate according to an example of the present invention;

FIG. 11 is a sectional view showing an intermediate layer formed on asubstrate and a diamond-like carbon film formed thereon according toanother example of the present invention;

FIG. 12 is a schematic sectional view showing a conventional hard carbonfilm forming apparatus;

FIG. 13 illustrates the relations between partial pressures forsupplying Ar gas and values of film hardness in a method of forming ahard carbon film according to the present invention; and

FIG. 14 illustrates the relation between a self-bias developed in asubstrate and film hardness in the method of forming a hard carbon filmaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic sectional view showing an exemplary apparatus forforming a hard carbon film according to the present invention. Referringto FIG. 1, a plasma generation chamber 4 is provided in a vacuum chamber8. An end of a waveguide 2 is mounted on the plasma generation chamber4, while microwave supply means 1 is provided on another end of thewaveguide 2. A microwave that is generated in the microwave supply means1 passes through the waveguide 2 and a microwave inlet window 3, to beguided into the plasma generation chamber 4. The plasma generationchamber 4 is provided with a discharge gas inlet pipe 5 for introducinga discharge gas such as argon (Ar) gas into the plasma generationchamber 4. Further, a plasma magnetic field generator 6 is providedaround the plasma generation chamber 4. A plasma of high density isformed in the plasma generation chamber 4 by the actions of ahigh-frequency magnetic field formed by the microwave and a magneticfield generated by the plasma magnetic field generator 6.

A cylindrical substrate holder 12 is provided in the vacuum chamber 8.This cylindrical substrate holder 12 is rotatable about a shaft (notshown) which is arranged perpendicularly to wall surfaces of the vacuumchamber 8. A plurality of substrates 13 are mounted on a peripheralsurface of the substrate holder 12 at regular intervals. According tothis embodiment, 24 nickel (Ni) substrates 13 are mounted on theperipheral surface of the substrate holder 12. A high-frequency powersource 10 is connected to the substrate holder 12.

A cylindrical shielding cover 14 of a metal is provided around thesubstrate holder 12 at a prescribed distance. This shielding cover 14 isconnected to a ground electrode. This shielding cover 14 is adapted toprevent discharge across portions of the substrate holder 12 other thanthose intended for film formation and the vacuum chamber 8 caused by theRF voltage that is applied to the substrate holder 12 in formation ofthe films. The substrate holder 12 and the shielding cover 14 are soarranged that the distance therebetween is not more than the mean freepath of gas molecules. The mean free path of the gas molecules is lessthan or equal to the mean distance that ions and electrons that aregenerated by some cause and accelerated by an electric field can travelwith no collision. The distance between the substrate holder 12 and theshielding cover 14 is set to be not more than the mean free path of thegas molecules, so as to reduce the probability that ions and electronswill collide with the gas molecules, thereby preventing a chainprogression of ionization.

The distance between the substrate holder 12 and the shielding cover 14is preferably set to be not more than 1/10 of the mean free path of thegas molecules, in particular. According to this embodiment, the distancebetween the substrate holder and the shielding cover 14 is set at about5 mm, which is not more than 1/10 of the mean free path of the gasmolecules.

The shielding cover 14 has an opening 15. The plasma is drawn from theplasma generation chamber 4 and passes through the opening 15, to beemitted toward the respective substrate 13 mounted on the substrateholder 12 at a position at the opening 15. The vacuum chamber 8 isprovided therein with a reaction gas inlet pipe 16. A forward end of thereaction gas inlet pipe 16 is located above the opening 15. FIG. 2 is aplan view showing a portion around the forward end of the reaction gasinlet pipe 16. Referring to FIG. 2, the reaction gas inlet pipe 16includes a gas inlet part 16a for introducing CH₄ gas into the vacuumchamber 8 from the exterior, and a gas discharge part 16bperpendicularly connected with the gas inlet part 16a. The gas dischargepart 16b is arranged perpendicularly to a direction A of rotation of thesubstrate holder 12, to be positioned upstream of the direction ofrotation above the opening 15. The gas discharge part 16b is providedwith a plurality of holes 21 which are downwardly directed at an angleof about 45°. According to this embodiment, eight holes 21 are providedat spacing intervals that are gradually made narrower from the centertoward both sides. Thus, the CH₄ gas which is introduced from the gasinlet part 16a is substantially uniformly discharged from the respectiveholes 21.

An example for forming diamond-like carbon films serving as hard carbonfilms on nickel substrates through the apparatus shown in FIG. 1 is nowdescribed.

First, 24 Ni substrates 13 were mounted on the peripheral surface of thesubstrate holder 12 at regular intervals. Then, the vacuum chamber 8 wasevacuated to 10⁻⁵ to 10⁻⁷ Torr, and the substrate holder 12 was rotatedat a speed of about 10 rpm. Then, Ar gas was supplied from the dischargegas inlet pipe 5 of an ECR plasma generator at 5.7×10⁻⁴ Torr, while amicrowave of 2.45 GHz frequency and 100 W power was supplied from themicrowave supply means 1, so that an Ar plasma formed in the plasmageneration chamber 4 was emitted onto the surface of each substrate 13.At the same time, an RF voltage of 13.56 MHz frequency was applied tothe substrate holder 12 from the high-frequency power source 10, so thata self-bias developed in each substrate 13 was -20 V. CH₄ gas wassupplied from the reaction gas inlet pipe 16 at 1.3×10⁻³ Torr. The CH₄gas supplied from the reaction gas inlet pipe 16 was decomposed by anaction of the plasma so that carbon entered an ionic or neutral activestate having high reactivity to be emitted onto the surface of eachsubstrate 13.

The aforementioned step was carried out for about 15 minutes, to form adiamond-like carbon film of 1200 Å in thickness on the surface of eachsubstrate 13. FIG. 10 is a sectional view showing a diamond-like carbonfilm formed on each substrate 13 in the aforementioned manner. Referringto FIG. 10, a diamond-like carbon film 21 is formed on the substrate 13.

FIG. 3 illustrates the relation between a film forming time and asubstrate temperature in the aforementioned Example (hereinafterreferred to as "Example 1"), in comparison to data of a comparativeexample 1 in which diamond-like carbon films were formed similarly toExample 1 except that the substrate holder was not rotated, and acomparative example 2 in which diamond-like carbon films were formed inan apparatus without a shielding cover and without rotation of asubstrate holder. As understood from FIG. 3, the substrate temperaturewas about 45° C. in Example 1 at a time 15 minutes after starting filmformation, while the substrate temperatures at that same point in timein comparative examples 1 and 2 were about 60° C. and about 150° C.respectively. The substrate temperature was extremely increased incomparative example 2, conceivably because discharge was caused betweenthe vacuum chamber and portions of the substrate holder other than thosefor forming the films. The substrate temperature in comparative example1 was lower than that in comparative example 2, which shows that it ispossible to reduce the substrate temperature by providing the shieldingcover. The substrate temperature in Example 1 was lower than that incomparative example 1, conceivably because in Example 1, the portionsheated by plasma discharge were successively moved as the substrateholder was rotated, to suppress the increase in substrate temperature.According to the present invention, it is possible to select the type ofthe substrates without consideration of heat resistance, since theincrease of the substrate temperature can be suppressed.

The apparatus shown in FIG. 1 was employed to apply RF voltages tosubstrates so that self-biases developed in the substrates were -50 Vwhile CH₄ gas was supplied from the reaction gas inlet pipe at partialpressures of 3.0×10⁻⁴ Torr, 1.0×10⁻³ Torr and 1.3×10⁻³ Torrrespectively, for investigating the relations between the partialpressures and values of hardness of the resulting diamond-like carbonfilms as formed.

FIG. 13 illustrates the relations between the partial pressures forsupplying Ar gas and the values of Vickers hardness of the films, whichwere measured on the basis of JIS G0202.

As shown in FIG. 13, the values of hardness of the films were about 3000Hv regardless of the partial pressures for supplying Ar gas. Further,substantially similar results were obtained also when the partialpressures for supplying CH₄ gas were changed. Thus, it is understood tobe possible to form diamond-like carbon films having prescribed valuesof film hardness on substrates regardless of the partial pressures forsupplying Ar gas and CH₄ gas.

Then, the Ar gas and the CH₄ gas were supplied at partial pressures of5.7×10⁻⁴ Torr and 1.0×10⁻³ Torr respectively, while the output from thehigh-frequency power source was changed to vary the self-biasesdeveloped in the substrates. FIG. 14 illustrates the relation betweenthe self-bias developed in each substrate and film hardness of thediamond-like carbon film as formed.

As shown in FIG. 14, the film hardness was at a low value of about 500Hv when the self-bias developed in each substrate was 0 V. The filmhardness increased correspondingly with the absolute value of theself-bias voltage as it varied through the range of 0 V to -20 V. Thefilm hardness was at a high value of about 3000 Hv when the self-biaswas -20 V. This film hardness of about 3000 Hv substantially remainedunchanged when the self-bias was reduced below -20 V. Thus, it isunderstood that it is possible to form diamond-like carbon films ofabout 3000 Hv in hardness on substrates by setting the RF voltage of thehigh-frequency power source so that the self-bias developed in eachsubstrate is not more than -20 V, regardless of the partial pressuresfor supplying Ar gas and CH₄ gas.

A result similar to that shown in FIG. 14 was obtained also when thepartial pressures for supplying Ar gas and CH₄ gas were varied in arange of 1.0×10⁻⁴ to 20.0×10⁻⁴ Torr.

Another embodiment, for forming intermediate layers on substrates andthen forming diamond-like carbon films serving as hard carbon films onthe intermediate layers, will now be described.

FIG. 11 is a sectional view showing an intermediate layer 22 formed on asubstrate 13, and a hard carbon film 21 formed on this intermediatelayer 22.

FIG. 4 is a schematic sectional view showing a hard carbon film formingapparatus according to this embodiment of the present invention.Referring to FIG. 4, a shielding cover 44 is provided around a substrateholder 12 which is arranged in a vacuum chamber 8. This shielding cover44 is provided with first and second openings 45 and 43. According tothis embodiment, the first and second openings 45 and 43 are formed insubstantially opposite positions. The first opening 45 is formedsimilarly to the opening 15 shown in FIG. 1, so that a forward end of areaction gas inlet pipe 16 is located above the first opening 45,similarly to the apparatus shown in FIG. 1.

An evaporation source 41 is provided under the second opening 43, forevaporating material atoms for forming intermediate layers by anelectron beam and emitting the same toward substrates 13. An ion gun 42is provided in the vicinity of the evaporation source 41, for emittingions of an inert gas for supplying the material atoms evaporated fromthe evaporation source 41 with energy. According to this embodiment, theinert gas is Ar gas, and the intermediate layer forming means comprisethe evaporation source 41 and the ion gun 42. The evaporation source 41and the ion gun 42 emit the material atoms for forming intermediatelayers onto the substrates 13 through the second opening 43.

Other structures of this embodiment are similar to those of theembodiment shown in FIG. 1. Thus, elements corresponding to those inFIG. 1 are denoted by the same reference numerals, and a redundantdescription thereof is omitted.

Another inventive example will now be described, namely an example forforming intermediate layers from a single element, and then formingdiamond-like carbon films on the intermediate layers.

Similarly to the above described Example 1, 24 Ni substrates 13 weremounted on a peripheral surface of the substrate holder 12 at regularintervals. The vacuum chamber 8 was evacuated to 10⁻⁵ to 10⁻⁷ Torr, andthe substrate holder 12 was rotated at a speed of about 10 rpm. Then,the ion gun 42 was supplied with Ar gas, so that Ar ions were ejectedand emitted onto the surface of each substrate 13. At this time, the Arions were set at an acceleration voltage of 400 eV and ion currentdensity of 0.3 mA/cm². Simultaneously with the emission of the Ar ions,the evaporation source 41 was driven to evaporate Ru atoms, for emittingthe same onto the surface of each substrate 13. The Ru evaporation ratewas set to be 420 Å/min. in terms of a film forming rate on eachsubstrate 13.

The aforementioned step was carried out for about 5 minutes, to form anintermediate layer of Ru having a thickness of 200 Å on the surface ofeach substrate 13.

Then, the emission of Ru atoms from the evaporation source 41 and theemission of Ar ions from the ion gun 42 were stopped, and thereafter Argas was supplied from a discharge gas inlet pipe 5 of an ECR plasmagenerator at 5.7×10⁻⁴ Torr while a microwave of 2.45 GHz frequency and100 W power was supplied from microwave supply means 1, to emit an Arplasma formed in a plasma generation chamber 4 onto the surface of eachsubstrate 13. At the same time, an RF voltage of 13.56 MHz frequency wasapplied from a high-frequency power source 10 to the substrate holder 12and CH₄ was supplied from a reaction gas inlet pipe 16 at 1.3×10⁻³ Torr,so that a self-bias of -20 V developed in each substrate 13.

The aforementioned step was carried out for about 15 minutes, to form adiamond-like carbon film of 1200 Å in thickness on the intermediatelayer that had been formed on each substrate 13.

As a result of the aforementioned two steps, a layered thin filmincluding the intermediate layer 22 of Ru formed on the surface of eachsubstrate 13 and the diamond-like carbon film 21 formed on theintermediate layer 22, was obtained as shown in FIG. 11.

Due to such formation of the intermediate layer 22, it is possible torelax stress in the diamond-like carbon film 21, thereby improving theadhesion between the substrate 13 and the diamond-like carbon film 21.The stress in the diamond-like carbon film 21 can be relaxed conceivablybecause it is possible to relax thermal stress caused by a difference inthermal expansion coefficients between the substrate 13 and thediamond-like carbon film 21, due to the presence of the intermediatelayer 22.

Another inventive example will now be described, namely an example forforming mixed layers of material atoms and carbon as intermediate layersand then forming diamond-like carbon films thereon. In this example, anapparatus similar to that shown in FIG. 4 was employed.

Similarly to the above described Example 1, 24 Ni substrates 13 weremounted on the peripheral surface of the substrate holder 12 at regularintervals. The vacuum chamber 8 was evacuated to 10⁻⁵ to 10⁻⁷ Torr, andthe substrate holder 12 was rotated at a speed of about 10 rpm.

Then, Ar gas was supplied from the discharge gas inlet pipe 5 of the ECRplasma generator at 5.7×10⁻⁴ Torr, while a microwave of 2.45 GHzfrequency and 100 W power was supplied from the microwave supply means 1to emit an Ar plasma formed in the plasma generation chamber 4 onto thesurface of each sub-strate 13. At the same time, an RF voltage of 13.56MHz frequency was applied to the substrate holder 12 from thehigh-frequency power source 10 while CH₄ gas was supplied from thereaction gas inlet pipe 16, so that a self-bias of -20 V was developedin each substrate 13. The supply quantity of the CH₄ gas was graduallyincreased with time as shown in FIG. 5, to be 100 sccm, i.e., 1.3×10-3Torr, after a lapse of 5 minutes.

Simultaneously with the aforementioned film formation by the ECR plasmagenerator, Ar ions were emitted from the ion gun 42 and Ru atoms wereemitted from the evaporation source 41 to the surface of each substrate13. At this time, the Ar ions were set at an acceleration voltage of 400eV and ion current density of 0.3 mA/cm². Further, the Ru evaporationrate was gradually reduced with time from 420 Å/min. in terms of a filmforming rate on each substrate 13 to reach 0 Å/min. after a lapse of 5minutes, as shown in FIG. 6. The emission of the Ar ions from the iongun 42 was stopped when the Ru evaporation rate reached 0 Å/min., i.e.,after a lapse of 5 minutes.

As hereinabove described, carbon film formation by plasma CVD and Ruevaporation were simultaneously carried out in the first and secondopenings 45 and 43 respectively, to form an intermediate layercontaining Ru and C in a mixed state. According to this Example, theaforementioned step was carried out for about 5 minutes, to form a mixedlayer of Ru and C having a total thickness of 200 Å on the surface ofeach substrate 13. As shown in FIGS. 5 and 6, the evaporation volume ofRu was reduced and the amount of carbon film formation was increasedwith time. Thus, the intermediate layer had a graded structure orcomposition gradient such that the Ru content was gradually reduced andthe C content was gradually increased as the distance from the surfaceof each substrate 13, increased.

Then, a diamond-like carbon film was formed on each intermediate layer.CH₄ gas was supplied from the reaction gas inlet pipe 16 at a constantpartial pressure of 1.3×10⁻³ Torr, to continuously carry out filmformation by the ECR plasma generator in the aforementioned step. Thisstep was carried out for about 15 minutes, to form a diamond-like carbonfilm of 1200 Å in thickness on the intermediate layer that had beenformed on each substrate 13.

As a result, a layered film including an intermediate layer consistingof Ru and C having a graded structure and a diamond-like carbon film wasformed on each substrate 13. Such an intermediate layer having a gradedstructure can further improve the adhesion between the substrate and thediamond-like carbon film as compared with the aforementionedintermediate layer consisting of a single element.

An evaluation test was conducted to evaluate the adhesion ofdiamond-like carbon films formed by the apparatus of the aforementionedembodiment. Samples were prepared by directly forming diamond-likecarbon films on Ni substrates (Example 1), by forming intermediatelayers consisting of Ru on Ni substrates and then forming diamond-likecarbon films on the intermediate layers (Example 2), by formingintermediate layers of mixed layers consisting of Ru and C on Nisubstrates and then forming diamond-like carbon films on theintermediate layers (Example 3), and by employing an Si evaporationsource for forming intermediate layers consisting of Si on Ni substratesand then forming diamond-like carbon films on the intermediate layers(Example 4). Adhesion was evaluated by an indentation test with constantloads (1 kg) employing Vickers indenters. 50 samples were prepared foreach Example, and the numbers of those causing separation of thediamond-like carbon films formed on the Ni substrates were counted.Table 1 shows the results.

                  TABLE 1                                                         ______________________________________                                               Example 1                                                                             Example 2 Example 3 Example 4                                  ______________________________________                                        Number of                                                                              43        7         0       16                                       Samples                                                                       Causing                                                                       Separation                                                                    ______________________________________                                    

As obvious from Table 1, the numbers of samples causing separation werereduced in Examples 2, 3 and 4, which were provided with theintermediate layers, as compared with Example 1, which was not providedwith an intermediate layer. Thus, it is understood that it is possibleto improve the adhesion of the diamond-like carbon films by providingthe intermediate layers. Particularly from Example 3, it is clearlyunderstood that it is possible to remarkably improve the adhesion of thediamond-like carbon films by forming the intermediate layers of Ru and Chaving graded structures.

Comparing Examples 2 and 4 with each other, it is understood that Ru issuperior to Si as material atoms for forming intermediate layers withrespect to Ni substrates.

FIG. 7 is a schematic sectional view showing a hard carbon film formingapparatus according to still another embodiment of the presentinvention. Referring to FIG. 7, a shielding cover 44 is provided arounda substrate holder 12 which is arranged in a vacuum chamber 8. Theshielding cover 44 has a first opening 45 similar to the opening 15shown in FIG. 1, so that a forward end of a reaction gas inlet pipe 16is located above the first opening 45, similarly to the apparatus shownin FIG. 1.

A target 46 of material atoms for forming intermediate layers isprovided under a second opening 43 of the shielding cover 44. Further,an ion gun 47 is provided in the vicinity of the target 46, for emittingions of an inert gas to the target 46 thereby sputtering the target 46.According to this embodiment, the inert gas is Ar gas and theintermediate layer forming means comprises the target 46 and the ion gun47, while thin-film heads 48 are mounted on the substrate holder 12 assubstrates. The target 46 and the ion gun 47 emit the material atoms forforming intermediate layers onto the thin-film heads 48 through thesecond opening 43.

The ions from the ion gun 47 are applied not only to the target 46 butalso to the thin-film head 48.

Other structures of this embodiment are similar to those of theembodiment shown in FIG. 1. Thus, elements corresponding to those inFIG. 1 are denoted by the same reference numerals, and a redundantdescription is omitted.

A further inventive example will now be described, namely an example forforming intermediate layers from a single element, and then formingdiamond-like carbon films thereon.

Similarly to the above described Example 1, 24 thin-film heads 48 weremounted on a peripheral surface of the substrate holder 12 at regularintervals. The vacuum chamber 8 was evacuated to 10⁻⁵ to 10⁻⁷ Torr, andthe substrate holder 12 was rotated at a speed of about 10 rpm. Then, Argas was supplied to the ion gun 47, so that Ar ions were ejected andemitted onto a surface of the target 46 consisting of Si. At this time,the Ar ions were set at an acceleration voltage of 900 eV and ioncurrent density of 0.3 mA/cm².

The aforementioned step was carried out for about 2 minutes, to form anintermediate layer of Si having a thickness of 60 Å on the surface ofeach thin-film head 48.

Then, the emission of the Ar ions from the ion gun 47 was stopped and Argas was supplied from a discharge gas inlet pipe 5 of an ECR plasmagenerator at 5.7×10⁻⁴ Torr, while a microwave of 2.45 GHz frequency and100 W power was supplied from microwave supply means 1, to emit an Arplasma formed in a plasma generation chamber 4 onto the surface of eachthin-film head 48. At the same time, an RF voltage of 13.56 MHzfrequency was applied to the substrate holder 12 from a high-frequencypower source 10 and CH₄ gas was supplied from a reaction gas inlet pipe16 at 1.3×10⁻³ Torr, so that a self-bias of -20 V was developed in eachthin-film head 48.

The aforementioned step was carried out for about 2.5 minutes, to form adiamond-like carbon film of 200 Å in thickness on the intermediate layerthat had been formed on each thin-film head 48.

As a result of the aforementioned two steps, a layered thin film wasformed on the surface of each thin-film head 48, including theintermediate layer of Si and the diamond-like carbon film formedthereon. Due to such formation of an intermediate layer, it is possibleto relax stress in a diamond-like carbon film, thereby improving theadhesion between a substrate and the diamond-like carbon film. Thestress in the diamond-like carbon film can be relaxed conceivablybecause it is possible to relax the thermal stress caused by thedifference in thermal expansion coefficients between the substrate andthe diamond-like carbon film, due to the presence of the intermediatelayer. Further, the intermediate layer is formed with higher adhesionsince the Ar ions are applied not only to the target but also to eachthin-film head during formation of the intermediate layer.

Another inventive example will now be described, namely an example forforming mixed layers of material atoms and carbon as intermediate layersand forming diamond-like carbon films thereon. Also in this example, anapparatus similar to that shown in FIG. 7 was employed.

First, 24 thin-film heads 48 were mounted on the peripheral surface ofthe substrate holder 12 at regular intervals. The vacuum chamber 8 wasevacuated to 10⁻⁵ to 10⁻⁷ Torr, and the substrate holder 12 was rotatedat a speed of about 10 rpm.

Then, Ar gas was supplied from the discharge gas inlet pipe 5 of the ECRplasma generator at 5.7×10⁻⁴ Torr while a microwave of 2.45 GHzfrequency and 100 W power was supplied from the microwave supply means1, to emit an Ar plasma formed in the plasma generation chamber 4 to thesurface of each thin-film head 48. At the same time, an RF voltage of13.56 MHz frequency was applied from the high-frequency power source 10to the substrate holder 12 and CH₄ gas was supplied from the reactiongas inlet pipe 16, so that a self-bias of -20 V was developed in eachthin-film head 48. At this time, the supply quantity of the CH₄ gas wasgradually increased with time to reach 100 sccm, i.e., 1.3×10⁻ Torr,after a lapse of 3 minutes, as shown in FIG. 8.

Simultaneously, with the film formation by the ECR plasma generator, Arions were emitted onto the surface of the target 46 from the ion gun 47.At this time, the Ar ions were set at an acceleration voltage of 900 eVand ion current density of 0.3 mA/cm².

The ion current density was gradually reduced with time to reach 0mA/cm² after a lapse of 3 minutes, as shown in FIG. 9.

As hereinabove described, carbon film formation by plasma CVD and Sisputtering were simultaneously carried out in the first and secondopenings 45 and 43 respectively, to form a mixed layer of Si and C as anintermediate layer. According to this embodiment, the aforementionedstep was carried out for about 3 minutes, to form a mixed layer of Siand C having a total thickness of 60 Å on the surface of each thin-filmhead 48. As shown in FIGS. 8 and 9, the quantity of Si was reduced andthe amount of carbon film formation was increased over time. Thus, thisintermediate layer had a graded structure or composition gradient suchthat the Si content was gradually reduced and the C content wasgradually increased as the distance from the surface of each thin-filmhead 48 increased.

Then, a diamond-like carbon film was formed on each intermediate layer.CH₄ gas was supplied from the reaction gas inlet pipe 16 at a constantpartial pressure of 1.3×10⁻³ Torr, to continuously carry out filmformation by the ECR plasma generator in the aforementioned step. Thisstep was carried out for about 2.5 minutes, to form a diamond-likecarbon film of 200 Å in thickness on the intermediate layer of eachthin-film head 48.

As a result, a layered film including the intermediate layer of Si and Chaving a graded structure and the diamond-like carbon film was formed oneach substrate. Such an intermediate layer having a graded compositionor structure can further improve the adhesion between the substrate andthe diamond-like carbon film as compared with the aforementionedintermediate layer consisting of a single element.

A further inventive example will now be described, namely an example forforming intermediate layers mainly composed of Si on Ni substrates andthen forming diamond-like carbon films on the intermediate layersaccording to the second aspect of the present invention through theapparatus shown in FIG. 7.

The vacuum chamber 8 was evacuated to 10⁻⁵ to 10⁻⁷ Torr, and thesubstrate holder 12 was rotated at a speed of about 10 rpm. 24 Nisubstrates were mounted on the substrate holder 12 at regular intervals.The ion gun 47 was supplied with Ar gas, to emit Ar ions onto thesurface of the target 46. At this time, the Ar ions were set at anacceleration voltage of 900 eV and ion current density of 0.3 mA/cm²,while the sputtered Si was evaporated on each substrate at anevaporation rate of 30 Å/min.

The time for the Si sputtering step was changed to vary the thicknessesof the Si intermediate layers formed on the Ni substrates to 30 Å, 50 Å,100 Å and 500 Å (Example 5).

Diamond-like carbon films of 1200 Å in thickness were formed similarlyto Example 1 on the intermediate layers having different thicknesses,which were obtained in the aforementioned manner.

An evaluation test for adhesion was carried out on the diamond-likecarbon films obtained in the aforementioned manner. The adhesionevaluation test was carried out similarly to that for Examples 1 to 4described above.

Table 2 shows the results.

                  TABLE 2                                                         ______________________________________                                                         Example 5                                                               Example 1                                                                             30Å 50Å                                                                              100Å                                                                           500Å                               ______________________________________                                        Number of Samples                                                                          43        16      0    0    0                                    Causing Separation                                                            ______________________________________                                    

As clearly understood from Table 2, the diamond-like carbon films weregenerally separated when the intermediate layers were less than 50 Å inthickness, while no such separation was recognized when the filmthicknesses exceeded 50 Å.

It is conceivable that a sufficient range for the thickness of theintermediate layer is up to about 5000 Å when thehard-carbon-film-coated substrate according to the present invention isapplied to an outer blade of an electric shaver. The adhesion is notfurther improved even if the thickness exceeds 5000 Å. Therefore, it isconceivable that a thickness of about 4000 Å is sufficient for anintermediate layer that is mainly composed of Si in the presentinvention. It is also conceivable that a thickness of about 5000 Å issufficient for the diamond-like carbon film. If the thickness of thediamond-like carbon film exceeds 5000 Å, then internal stress couldeasily be caused and deform the substrate as a result.

Another inventive example will now be described, namely an example forforming mixed layers of Si and carbon as intermediate layers.

Mixed layers of Si and carbon were formed similarly to theaforementioned Example for forming mixed layers of Si and C asintermediate layers. Samples were prepared by varying the thicknesses ofthe intermediate layers to 30 Å, 50 Å, 100 Å and 500 Å (Example 6).Further, diamond-like carbon films were formed on the intermediatelayers to a thickness of 1200 Å. Adhesion of the diamond-like carbonfilms was evaluated in the samples obtained in the aforementionedmanner, similarly to the above.

Table 3 shows the results.

                  TABLE 3                                                         ______________________________________                                                         Example 6                                                               Example 1                                                                             30Å 50Å                                                                              100Å                                                                           500Å                               ______________________________________                                        Number of Samples                                                                          43        14      0    0    0                                    Causing Separation                                                            ______________________________________                                    

As clearly understood from Table 3, the diamond-like carbon films weregenerally separated when the intermediate layers of SiC were less than50 Å in thickness, while no such separation was recognized when the filmthicknesses exceeded 50 Å. Thus, the intermediate layer is preferably atleast 50 Å in thickness, also when the intermediate layer is preparedfrom SiC.

Then, nitrogen gas was introduced as a reaction gas containing nitrogenfrom the gas inlet pipe 16 shown in FIG. 7 into the vacuum chamber 8, toform mixed layers of Si and nitrogen as intermediate layers. Thenitrogen gas was supplied at a partial pressure of 1.8×10⁻⁴ Torr.Diamond-like carbon films were formed on the intermediate layers, underconditions similar to those in Example 6. Consequently, results similarto those shown in Table 3 were obtained.

Further, mixed layers of Si and oxygen were formed as intermediatelayers, and then diamond-like carbon films were formed on theseintermediate layers. A reaction gas containing oxygen was prepared fromoxygen gas, and supplied at a partial pressure of 1.8×10⁻⁴ Torr.Diamond-like carbon films were formed on the intermediate layers, underconditions similar to those in Example 6. Consequently, results similarto those shown in Table 3 were obtained.

Further, Ge was employed in place of Si as an intermediate layer. Theevaluation of adhesion was performed similarly to Examples 5 and 6.Consequently, results similar to those shown in Tables 2 and 3 wereobtained.

An example according to the third aspect of the present invention willnow be described. According to this example, carbon thin films wereformed as intermediate layers. An apparatus similar to that shown inFIG. 7 was employed for forming the carbon thin films, with a carbontarget. Ar ions were set at an acceleration voltage of 900 eV and ioncurrent density of 0.3 mA/cm². The times for forming the carbon thinfilms were changed to vary the thicknesses of the carbon thin filmsserving as intermediate layers to 30 Å, 50 Å, 100 Å and 500 Å (Example7). Diamond-like carbon films were formed on the intermediate layershaving different thicknesses obtained in the aforementioned manner,similarly to the above Example 5, and then were subjected to an adhesionevaluation test. Table 4 shows the results.

                  TABLE 4                                                         ______________________________________                                                         Example 7                                                               Example 1                                                                             30Å 50Å                                                                              100Å                                                                           500Å                               ______________________________________                                        Number of Samples                                                                          43        15      0    0    0                                    Causing Separation                                                            ______________________________________                                    

As clearly understood from Table 4, the diamond-like carbon films weregenerally separated when the intermediate layers were less than 50 Å inthickness, while no such separation was recognized when the filmthicknesses exceeded 50 Å. Thus, the intermediate layer is preferably atleast 50 Å in thickness, also when the layer is formed by a carbon thinfilm. Further, the intermediate layer is preferably not more than 4000 Åin thickness when the hard-carbon-film-coated substrate is used for anouter blade of an electric shaver, while it is preferably not more than8000 Å in thickness when the hard-carbon-film-coated substrate is usedfor an inner blade, for reasons similar to those discussed aboveregarding the example according to the second aspect of the presentinvention.

In the present invention, an intermediate layer may be formed by plasmaCVD. In this case, a gas containing material atoms for forming anintermediate layer is supplied into a vacuum chamber 8 from a reactiongas inlet pipe 16 to form a plasma and emit the plasma toward asubstrate thereby forming the intermediate layer on the substrate.

While each of the above embodiments and examples has been described withreference to an ECR plasma generator serving as plasma generation means,the present invention is not restricted to this but another plasma CVDapparatus such as a high-frequency plasma CVD apparatus or a DC plasmaCVD apparatus is also employable.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A hard-carbon-film-coated substrate comprising:asubstrate consisting of a metal or an alloy at least mainly composed ofNi or Al, or stainless steel; an intermediate layer at least mainlycomposed of Ru arranged on said substrate; and a predominantly amorphoushard carbon film arranged on said intermediate layer.
 2. Thehard-carbon-film-coated substrate in accordance with claim 1, whereinsaid hard carbon film is a diamond-like carbon film.
 3. Thehard-carbon-film-coated substrate in accordance with claim 1, whereinsaid hard carbon film has a Vickers hardness of about
 3000. 4. Thehard-carbon-film-coated substrate in accordance with claim 1, whereinsaid intermediate layer provides an improved adhesion of said hardcarbon film through said intermediate layer onto said substrate ascompared to an adhesion of said hard carbon film directly onto saidsubstrate.
 5. The hard-carbon-film-coated substrate in accordance withclaim 1, wherein said intermediate layer essentially consists of Ru. 6.A hard-carbon-film-coated substrate comprising:a substrate consisting ofa metal or an alloy at least mainly composed of Ni or Al, or stainlesssteel; an intermediate layer at least mainly composed of Si arrangeddirectly on and in contact with said substrate; and a predominantlyamorphous hard carbon film arranged on said intermediate layer.
 7. Ahard-carbon-film-coated substrate in accordance with claim 6, whereinsaid intermediate layer has a thickness of 50 to 8000 Å.
 8. Ahard-carbon-film-coated substrate in accordance with claim 6, whereinsaid intermediate layer has a thickness of 50 to 4000 Å.
 9. Thehard-carbon-film-coated substrate in accordance with claim 6, whereinsaid hard carbon film is a diamond-like carbon film.
 10. Thehard-carbon-film-coated substrate in accordance with claim 6, whereinsaid hard carbon film has a Vickers hardness of about
 3000. 11. Thehard-carbon-film-coated substrate in accordance with claim 6, whereinsaid intermediate layer provides an improved adhesion of said hardcarbon film through said intermediate layer onto said substrate ascompared to an adhesion of said hard carbon film directly onto saidsubstrate.
 12. The hard-carbon-film-coated substrate in accordance withclaim 6, wherein said intermediate layer essentially consists of Si. 13.A hard-carbon-film-coated substrate comprising:a substrate consisting ofa metal or an alloy at least mainly composed of Ni or Al, or stainlesssteel; an intermediate layer at least mainly composed of Ge arranged onsaid substrate; and a predominantly amorphous hard carbon film arrangedon said intermediate layer.
 14. A hard-carbon-film-coated substrate inaccordance with claim 13, wherein said intermediate layer has athickness of 50 to 8000 Å.
 15. A hard-carbon-film-coated substrate inaccordance with claim 13, wherein said intermediate layer has athickness of 50 to 4000 Å.
 16. The hard-carbon-film-coated substrate inaccordance with claim 13, wherein said hard carbon film is adiamond-like carbon film.
 17. The hard-carbon-film-coated substrate inaccordance with claim 13, wherein said hard carbon film has a Vickershardness of about
 3000. 18. The hard-carbon-film-coated substrate inaccordance with claim 13, wherein said intermediate layer provides animproved adhesion of said hard carbon film through said intermediatelayer onto said substrate as compared to an adhesion of said hard carbonfilm directly onto said substrate.
 19. The hard-carbon-film-coatedsubstrate in accordance with claim 13, wherein said intermediate layeressentially consists of Ge.